[net80211] document the (not completely complete) set of places where

we're assuming hz=1000 and not gracefully handling when it isn't.

The math involved will return 0 for hz < 1000, which it is on some
platforms and on DragonflyBSD.

This doesn't fix it, it:

* converts one manual use over to use the macro, and
* comments where it needs some thought/fixing.

I'll think about this a bit more before fixing it.

Submitted by:	imre@vdsz.com

sys/net80211/ieee80211_freebsd.h

@@ -246,9 +246,11 @@ void	ieee80211_vap_destroy(struct ieee80211vap *);
 	(((_ifp)->if_flags & IFF_UP) && \
 	 ((_ifp)->if_drv_flags & IFF_DRV_RUNNING))
 
+/* XXX TODO: cap these at 1, as hz may not be 1000 */
 #define	msecs_to_ticks(ms)	(((ms)*hz)/1000)
 #define	ticks_to_msecs(t)	(1000*(t) / hz)
 #define	ticks_to_secs(t)	((t) / hz)
+
 #define time_after(a,b) 	((long)(b) - (long)(a) < 0)
 #define time_before(a,b)	time_after(b,a)
 #define time_after_eq(a,b)	((long)(a) - (long)(b) >= 0)

sys/net80211/ieee80211_scan_sw.c

@@ -641,7 +641,7 @@ scan_task(void *arg, int pending)
 			 * XXX Should use M_TXCB mechanism to eliminate this.
 			 */
 			cv_timedwait(&SCAN_PRIVATE(ss)->ss_scan_cv,
-			    IEEE80211_LOCK_OBJ(ic), hz / 1000);
+			    IEEE80211_LOCK_OBJ(ic), msecs_to_ticks(1));
 			if (SCAN_PRIVATE(ss)->ss_iflags & ISCAN_ABORT)
 				goto done;
 		}

sys/net80211/ieee80211_var.h

@@ -84,6 +84,7 @@
 
 #define	IEEE80211_MS_TO_TU(x)	(((x) * 1000) / 1024)
 #define	IEEE80211_TU_TO_MS(x)	(((x) * 1024) / 1000)
+/* XXX TODO: cap this at 1, in case hz is not 1000 */
 #define	IEEE80211_TU_TO_TICKS(x)(((x) * 1024 * hz) / (1000 * 1000))
 
 /*